Protozoan Pathogens Flashcards
Entamoeba histolytica tissues invaded
Small intestine, can invade deeper tissues (liver, less commonly brain, lungs)
Proportion of infected in developing world
5-10% of population
Can entamoeba histolytica be asymptomatic?
Yes - many infections are asymptomatic
Entamoeba histolytica spread
Faecal-oral person-person spread
Entamoeba histolytica receptor
Digalactose residue on intestinal cells. Attaches with a surface lectin.
Entamoeba histolytica mechanisms for evading immune system:
1)
2)
1) Contact-dependent pore-forming toxin inserted into cells
2) Secretes factors which breaks down IgA, IgG
Immune mechanisms against entamoeba histolytica:
1)
2)
1) Mucus covers digalactose residues on intestinal cells
2) Cell-mediated immunity
Entamoeba histolytica pathogenesis:
1)
2)
3)
1) Binds to cells with surface lectin-digalactose residues
2) Contact-dependent pore-forming toxin inserted
3) Amoeba ingests lysed cell
Entamoeba histolytica treatment
Metronidazole
Entamoeba histolytica lab diagnosis:
1)
2)
3)
1) Look for cysts in stool sample (microscopy)
2) Stool immunoassay for parasite antigen
3) Serology of patient sera
- Can’t distinguish between recent infections
Entamoeba histolytica symptoms
Dysentary
Giardia lamblia symptoms
Watery diarrhoea, greasy, foul-smelling stools
Giardia lamblia transmission
Zoonosis. Transmitted from animals or infected humans
Diseases caused by giardia lamblia
Traveller’s diarrhoea
Difficulties in killing giardia lamblia
Acid-, chlorine-resistant
Giardia lamblia pathogenesis: 1) 2) 3) 4)
1) Cysts ingested
2) Excystation in small intestine, attach to intestinal wall with ventral sucking disc
3) Intestinal absorptive capacity decreased as increased numbers of trophozoites attach
4) Host responses include lymphocyte invasion of mucosal cells, shortening of microvilli
Giardia lamblia lab diagnosis:
1)
2)
1) Microscopy of stool samples
2) Antigen detection assay
Giardia lamblia treatment
Metronidazole
Cryptosporidium symptoms
Watery diarrhoea
Cryptosporidium life-cycle: 1) 2) 3) 4) 5)
1) Oocysts ingested (sporulated oocyst contains 4 sporozoites)
2) Excystation in GIT, parasitisation of epithelial cells
3) Asexual replication
4) Sexual replication
5) Thick-walled oocysts excreted, thin-walled oocysts autoinfection
Cryptosporidium sexual reproduction
Macrogamonts (F) fertilised by microgamonts (M)
Cryptosporidium virulence factors
Little known.
Surface glycoproteins and lectins involved
Doesn’t invade deeper than microvilli
Produces proteases
Cryptosporidium lab diagnosis
Microscopy for acid-fast cysts
Stool antigen detection assay
Cryptosporidium treatment
Nitazoxanide (similar to metronidazole)
